We are interested in characterizing the structures and biochemical properties of proteins involved in iron metabolism, with the assumption that biochemical and 3D structural information can be used to guide design of biological experiments to understand their function. We previously solved the crystal structures of HFE, a type I membrane protein that binds to transferrin receptor 1 (TfR1) and is mutated in the iron overload disease hereditary hemochromatosis, and an HFE/TfR1 complex. We now wish to combine our expertise in structural biology and biochemistry with the skills of Drs. Enns and Blackburn in cell biology and metalloprotein spectroscopy respectively, to study different aspects of metallobiology, with the goal of shedding new light on the function of a newly discovered transferrin receptor (TfR2). We have already demonstrated that a soluble form of TfR2 binds iron loaded transferrin (FeTf), but not HFE, at the pH of the cell surface. We now seek to further characterize the TfR2 interaction with Tf in order to compare and contrast the binding properties of TfR2 with those of TfR1. The aims of this project are to: (1) Examine the binding profiles of apo and diferric Tf to TfR2 compared to TfR1, with an emphasis on characterizing the pH dependence of the interactions in order to predict which intracellular compartments contain TfR2-Tf complexes, (2) Define the binding site on TfR2 for Tf by site directed mutagenesis and by a cross-linking, proteolysis and mass spectrometry approach (in collaboration with Dr. Enns), (3) Conduct structural studies of TfR2, the Tf-TfR2 complex and other interesting proteins coming out of these projects in collaboration with all of the investigators participating in this program project.